You are in a glass sphere suspended by a steel chain from the Empire State Building. With you in the sphere are a sugar cube and a small stone, and you are holding a pigeon. You will gain your freedom if you can make the sphere lighter using the pigeon. What is your best strategy for escape? (Note: the pigeon must remain inside the sphere at all times.)

Answer

Release the bird and make a small hole in the sphere with the stone. Simply releasing the bird will not decrease the weight of the sphere because the bird must exert pressure (downward force) on the air in the sphere to keep itself aloft, and the air in turn presses down on the sphere. However, if you make a hole of any kind in the sphere with the stone, some of the downward force of the air that is beaten down by the bird's wings will be dissipated outside the sphere, making the sphere lighter.Hide